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The case for the Ediacaran fossil roots to the Metazoan Tree
Abstract
The first challenge to the traditional interpretation of the Late Proterozoic Ediacara fossils came with a paper by A. Seilacher (1984, 1989) which not only proposed that Ediacaran organisms became extinct before the Cambrian, but that they represented a previously unrecognized kingdom of structurally unique multicellular organisms: the Vendozoa. This new model is based on a number of uncontested generalizations about size, shape, lifestyle and preservation, that have persisted in the literature. Many of these assumptions are now shown to be misconceptions, as a consequence of newly discovered material in Australia, Canada and the USSR, revealing a more diverse fossil assemblage and suggesting that the organisms were dominantly benthic. The interpretation of this biota in phylogenetic terms, is vindicated by the realization of strong links between some Ediacaran and Cambrian organisms. -from Author
... Parvancorina are benthic marine animals with other suggested from eolian beds and palaeosols of non-marine environmental conditions (Gehling 1991 (Glaessner 1958(Glaessner , 1979(Glaessner , 1980. Globally, two species of Parvancorina have been discussed: i.e., P. minchami (Glaessner 1958) and P. sagitta (Ivantsov et al. 2004). ...
... Parvancorina Ediacaran fossils are considered benthic marine organisms with euarthropod aDnities based on their bilateral symmetry with separated antero-posterior alignment (Gehling 1991;Lin et al. 2006;Sperling and Vinther 2010;LaCamme et al. 2013). Some workers compare these Parvancorina organisms with the Skania arthropod (Glaessner 1980;Gehling 1991;Lin et al. 2006) and Primicaris arthropod (Zhang et al. 2003) of the Cambrian Period based on its posterior anchor-shaped ridge on an unbroken bilateral body with rounded outline morphology. ...
... Parvancorina Ediacaran fossils are considered benthic marine organisms with euarthropod aDnities based on their bilateral symmetry with separated antero-posterior alignment (Gehling 1991;Lin et al. 2006;Sperling and Vinther 2010;LaCamme et al. 2013). Some workers compare these Parvancorina organisms with the Skania arthropod (Glaessner 1980;Gehling 1991;Lin et al. 2006) and Primicaris arthropod (Zhang et al. 2003) of the Cambrian Period based on its posterior anchor-shaped ridge on an unbroken bilateral body with rounded outline morphology. Later, these Parvancorina organisms were compared with the single-tagma protaspides, especially those trilobites whose anchor structure is connected to the glabella and eye ridges (Legg et al. 2015). ...
The present investigation documents and describes the anchor-shaped Ediacaran organisms assigned to Parvancorina (cf. P. minchami) on the sandstone bedding plane of Sonia Formation of Marwar Super-group in India. This is the Brst report of Parvancorina organisms from India. Specimens are preserved as small, rounded to ovate, posterior shield-shaped impressions with an anterior-lateral widened portion and a posterior anchor-shaped structure. P. minchami shows both positive and negative relief preservation modes. In Sonia Formation, the recovered P. minchami specimens have been found in size ranges of 1.5 9 1.5 to 3.0 9 3.5 cm 2 (length 9 width), suggesting preservation of adult and larger forms.
... The smallest distinguishable specimens of Dickinsonia are 1-2 mm long (Ivantsov & Zakrevskaya 2022). The average length of their body is a few centimetres, although there are known specimens that reach 1 metre in length (Gehling 1991;Jenkins 1992;Gehling et al. 2005) and possibly even bigger ones, reconstructed from fragments (Jenkins 1996). The length of the largest White Sea specimen of D. tenuis, which is not completely visible on the surface of the bearing layer, exceeds 55 cm. ...
... The structure as a whole can stand out rather sharply in the relief of imprints (Fig. 3a, c), but it disappears at a high degree of tissue decomposition (Fig. 1c). Apparently, it represented some kind of a band that lay inside the body of Dickinsonia (Wade 1972;Runnegar 1982;;Gehling 1991;Jenkins 1992;Evans et al. 2019а;Ivantsov & Zakrevskaya 2022). ...
... The nature of the linear axial structure of Dickinsonia is discussed here. It is hypothesised that the food-filled gut could have been preserved in this form (Wade 1972;Runnegar 1982;Gehling 1991;Jenkins 1992), but it is also believed that it was a mechanical artefact that arose during the process of fossilisation (Brasier & Antcliffe 2008) or that the axial structure, 'midline', was like a dense membrane to which the transverse elements were attached (Gehling et al. 2005;Evans et al. 2017). In one of their papers, Evans et al. (2019a) suggest that the 'midline' was filled with fluid and acted as a hydrostatic skeleton during the work of various muscles of Dickinsonia. ...
Materials collected on the territory of the southeastern White Sea area, including diversely preserved body imprints, combined body-trace fossils, specimens with signs of intravital damage and regeneration, and extended ontogenetic series, make it possible to significantly widen the data on the body plan and biology of Dickinsonia, the oldest known mobile animal, included in the Late Pre-cambrian taxon of high rank, Proarticulata. A number of reconstructed anatomical features were added to the obvious directly observed features of Dickinsonia, such as a consistent body shape lacking lateral appendages and temporary outgrowths, transverse differentiation, and anterior-posterior polarity. These reconstructed features include dorsoventral polarity, ciliated mucus-secreting epithelium underlain by a basal lamina, two rows of blind food-gathering pockets, absence of a through-gut, nervous system of diffusive type, axial support band and muscle fibres. Such a set of features indicates the affinity of Dickinsonia and Proarticulata as a whole (the only known Ediacaran Metazoa) to Urbilateria, a hypothetical ancestor of bilaterally symmetrical animals.
... Microfossils, microbialites (stromatolites, leiolites, thrombolites, dendrolites) and geochemical data are widely used to study the oldest traces of life (Schopf, 1999;Watanabe et al., 2000;Altermann & Kazmierczak, 2003). Recently, another taphonomic window has been developed based on actualistic comparisons with structures developed by the interaction of microbial mats, siliciclastic sediments and environmental conditions (Gehling, 1991;Eriksson et al., 2007). The combination of microbial mat activity (growth, bioprecipitation, and decay) and environmental conditions often can result in the formation of several biomat-related structures in siliciclastic sediments that can be preserved in the geological record. ...
... The combination of microbial mat activity (growth, bioprecipitation, and decay) and environmental conditions often can result in the formation of several biomat-related structures in siliciclastic sediments that can be preserved in the geological record. These are now collectively known as microbially induced sedimentary structures (MISS) Noffke, 2009;Sarkar et al., 2014;Davies et al., 2016;Gehling, 1991;Aref et al., 2020;Seilacher et al., 1994;Seilacher, 1999;Noffke, 2021). ...
The Eastern Anti-Atlas of Morocco hosts an early Ediacaran turbiditic series (Saghro Group) (630–600 Ma) unconformably overlain by thick late Ediacaran (580–550 Ma) terrestrial volcano-clastic formations (Ouarzazate Supergroup), with thin and geographically limited paralic shallow marine sedimentary rocks.
This paper presents the first description of structures related to the former presence of extensive microbial mats developed in marine, fluvial, and lacustrine environments during the Ediacaran in the Eastern Anti-Atlas. These microbially induced sedimentary structures (MISS) are largely found in well-laminated fine- to coarse-grained sandstone and sandy-carbonate. They also cover vast bedding planes and occur in almost all sedimentary successions. MISS types include: gas domes, wrinkle structures, reticulate patterns, overflips and roll-ups, multidirectional linear ridges, sand cracks and biolaminated deposits. Based on morphology and petrographic macro and microfabrics, these microbially induced structures are very similar to those of modern photosynthetic cyanobacteria mats. Together with previously reported stromatolites, these newly reported microbial mat structures could have played an important ecological role in stabilizing siliciclastic sediments, as well as sustaining localized zones of high oxygen production in the Ediacaran marine and terrestrial paleoenvironments of the Anti-Atlas. The widespread geographic distribution and consistent occurrence of microbially induced sedimentary structures (MISS) in fluvial and lacustrine sediments present compelling paleontological evidence supporting the extensive greening of the land surface during the late Precambrian period.
... The Precambrian life forms discovered, notably the Ediacara fauna, have been interpreted as several distinct members of the Metazoa crown group (Gehling, 1991;Dzik, 2003;Waggoner, 2003); some organisms have been interpreted as microbial colonies, or even lichens (Peterson et al., 2003;MacGabhann, 2007;Retallack, 2012Retallack, , 2013. It has also been proposed the denomination of vendobionts for these organisms which could constitute a separate phylum, today without descendants (Seilacher, 1989(Seilacher, , 1992Buss et Seilacher, 1994;Xiao et Laflamme, 2009;Dunn et al., 2018). ...
... There are various interpretations as to the nature of these fossils; some researchers (Gehling, 1991) believe that these organisms could be the oldest sponges, but this theory is not accepted by most scientists. Another hypothesis (Sepkoski et al., 2002) sees Rugoconites as a representative of cnidarians, such as a jellyfish; Ivantstov and Fedonkin (2003) hypothesized that it must be a representative of trilobozoans, a mysterious group of triradiate-symmetric bodies of uncertain affinity. ...
... Though it is relatively common in fossiliferous Ediacaran rocks of South Australia, Aulozoon evaded formal description until recently due to a long history of contradicting identifications as various forms of back stuffed or mucus lined burrows (Glaessner, 1969;Jenkins, 1995;Seilacher et al., 2003;Seilacher, 2007), and as fungal rhizomorphs (Retallack, 2007(Retallack, , 2013. Several studies have interpreted Aulozoon as a metazoangrade body fossil (Gehling, 1991;Fedonkin and Runnegar, 1992;Runnegar, 1994;Ivantsov, 2011;Droser et al., 2006), which was confirmed in the formal description of Aulozoon by Gehling and Runnegar (2022). ...
... Nevertheless, these efforts were overwhelmingly focused on the subsequent 'explosion' of animal phyla in the early Cambrian, rather than the disappearance of Ediacaran soft-bodied organisms below the boundary. This is perhaps not surprising given that, prior to propositions by Seilacher (1984Seilacher ( , 1985Seilacher ( , 1989Seilacher ( , 1992, the Ediacara biota were overwhelmingly interpreted as belonging to extant metazoan groups (e.g., Glaessner, 1984;Gehling, 1991). As such, the fossil record of the E-C transition could be satisfactorily explained as the result of taphonomic biases towards the preservation of biomineral shells, Figure 1. ...
Since the 1980s, the existence of one or more extinction events in the late Ediacaran has been the subject of debate. Discussion surrounding these events has intensified in the last decade, in concert with efforts to understand drivers of global change over the Ediacaran–Cambrian transition and the appearance of the more modern-looking Phanerozoic biosphere. In this paper we review the history of thought and work surrounding late Ediacaran extinctions, with a particular focus on the last 5 years of paleontological, geochemical, and geochronological research. We consider the extent to which key questions have been answered, and pose new questions which will help to characterize drivers of environmental and biotic change. A key challenge for future work will be the calculation of extinction intensities that account for limited sampling, the duration of Ediacaran ‘assemblage’ zones, and the preponderance of taxa restricted to a single ‘assemblage’; without these data, the extent to which Ediacaran bioevents represent genuine mass extinctions comparable to the ‘Big 5’ extinctions of the Phanerozoic remains to be rigorously tested. Lastly, we propose a revised model for drivers of late Ediacaran extinction pulses that builds off recent data and growing consensus within the field. This model is speculative, but does frame testable hypotheses that can be targeted in the next decade of work.
... THE Ediacaran biota is the oldest and distinct group of macroscopic, morphologically complex eukaryotic organisms that flourished in the late Ediacaran period 1,2 . They are mainly soft-bodied organisms with unusual body plans 3 and have been historically interpreted as the evolutionary precursors of Cambrian organisms or animals, including annelids, cnidarians, arthropods and echinoderms 4,5 . Among these, many Ediacaran taxa have tri-radial symmetry or body plan 2,3 and occur as three elevated, equal-spaced features or forms such as lobes, bumps, ridges or canals, as well as some elements of threefold symmetry arranged or bound in a peripheral ring 2,6,7 . ...
Here we describe the Tribrachidium and Albumares
Ediacaran organisms belonging to phylum Trilobozoa
in the Sonia Sandstone of Marwar Supergroup, western
India. Between the two Ediacaran genera, Albumares
brunsae was the first to be discovered in India, while
Tribrachidium heraldicum was the first record from the
Marwar Supergroup. T. heraldicum is soft-bodied, dis�coidal or disc-shaped (in plane view) and slightly coni�cal-shaped (when found with up to 2 mm vertical relief)
with three elevated lobes (arms) or ridges bounded by
a well-defined peripheral ring. A. brunsae is soft-bodied,
flattened, low-relief, circular to sub-circular and with
a tri-lobed (three elevated arms/rays) shield having
branching rays that radiate outward from the centre to
the outer edge of the peripheral ring. Both Ediacaran
taxa occur here as convex or positive reliefs with tri�radial symmetry on medium to fine-grained sandstone
bedding planes in the Sursagar area and show the Flin�ders Ranges style of preservation.
Keywords: Albumares, Ediacaran organisms, sandstone,
Tribrachidium, trilobozoan
... THE Ediacaran biota is the oldest and distinct group of macroscopic, morphologically complex eukaryotic organisms that flourished in the late Ediacaran period 1,2 . They are mainly soft-bodied organisms with unusual body plans 3 and have been historically interpreted as the evolutionary precursors of Cambrian organisms or animals, including annelids, cnidarians, arthropods and echinoderms 4,5 . Among these, many Ediacaran taxa have tri-radial symmetry or body plan 2,3 and occur as three elevated, equal-spaced features or forms such as lobes, bumps, ridges or canals, as well as some elements of threefold symmetry arranged or bound in a peripheral ring 2,6,7 . ...
Here we describe the Tribrachidium and Albumares Ediacaran organisms belonging to phylum Trilobozoa in the Sonia Sandstone of Marwar Supergroup, western India. Between the two Ediacaran genera, Albumares brunsae was the first to be discovered in India, while Tribrachidium heraldicum was the first record from the Marwar Supergroup. T. heraldicum is soft-bodied, dis-coidal or disc-shaped (in plane view) and slightly conical shaped (when found with up to 2 mm vertical relief) with three elevated lobes (arms) or ridges bounded by a well-defined peripheral ring. A. brunsae is soft-bodied, flattened, low-relief, circular to sub-circular and with a tri-lobed (three elevated arms/rays) shield having branching rays that radiate outward from the centre to the outer edge of the peripheral ring. Both Ediacaran taxa occur here as convex or positive reliefs with tri-radial symmetry on medium to fine-grained sandstone bedding planes in the Sursagar area and show the Flin-ders Ranges style of preservation.
Almost fifteen years have passed since the printing of the first volume in the Italian language published by the Back to the Past Museum.
Encouraged by its success in Italy and abroad, we decided to publish the translated version in English the following year (The Back to the Past Museum Guide to TRILOBITES). This tome, enlarged with updated plates, became a best seller in the paleontological field, obtaining an important worldwide distribution and a particularly positive evaluation by the professional sector.
This overwhelmingly positive response allowed our project to continuously expand the museum’s collections. Additionally, we began implementing research campaigns (always respecting international rules and laws), started an intense collaboration with professionals in the field, and consequently, have published in high-impact scientific journals.
This new volume, compared to the previous one, has not only been enriched with new tables and iconographic sources but it has also been updated regarding the classification of trilobite orders in accordance with the latest interpretations and studies. Studies that will lead to new interpretations and, consequently, new reorganizations of families and genera within the class of trilobites.
What we hope is that this text will attract the interest of the “warned” collector, the professional or simply the passionate. We would also like to dedicate this work of ours to each one of them, in the hope of reinforcing the thin bridge that exists between public and private, both interdependent for study, field research, the discovery of new species and the evolution of scientific thought.
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